Furnace Not Heating in Atherton, CA | Bay Area HVAC Service

Furnace Not Heating in Atherton

On most homes a furnace that won't heat is one failed part in the ignition or safety chain: a cracked igniter, a fouled flame sensor, a limit switch tripped by a starved filter, a control board that lost a relay. The fix is usually a single component, not a new system. Atherton adds a layer to that, because a lot of these larger homes don't run on one furnace.

When a homeowner here says the heat is out, they often mean one part of the house went cold while another stays warm. On a home with more than one heating system, that pattern is its own diagnosis: the fault is local to one system or one zone's controls, not the gas supply or the thermostat platform feeding the whole house. The work is identifying which air handler and which board is actually at fault, and that takes someone who reads multi-zone controls instead of pulling the first easy part.

When the systems in a house are different ages, the failures spread out. It might be an igniter on the older unit serving the original section, a drifting control board on a newer zone, or a stuck zone damper that makes a heating zone feel dead even though the furnace is firing. We trace the real fault before we touch anything.

Common causes

One zone's air handler failed while others run. When a single wing goes cold, the cause is usually contained to that system: its igniter, flame sensor, or board. We identify which air handler serves the cold zone, then diagnose that unit specifically instead of touching the systems that are working fine.

Stuck or failed zone damper. On a zoned system a damper that won't open makes a room feel like the heat is dead even though the furnace is firing correctly. We check the damper motors and the zone panel to confirm whether the problem is heat production or heat distribution, because those are very different repairs.

Cracked hot surface igniter. The most common reason burners never light on a forced-air furnace. The igniter cracks from years of heat cycling and stops glowing. We meter it and replace it, $200 to $350. When a house has more than one unit, the older system is usually the first to need this.

Dirty flame sensor. Lights then shuts off within seconds: the flame sensor is carboned over and the board can't confirm flame, so it cuts gas for safety. Cleaning usually restores it; a pitted sensor gets replaced at $150 to $200.

Control board relay or zone-board fault. Over years of service, boards drift. A failed heat relay or a glitchy zone board can leave one system unable to call for or deliver heat. We test the board's outputs rather than condemning it on sight, since a board is one of the pricier furnace parts.

Limit switch tripped by a clogged filter. A starved filter overheats the heat exchanger and trips the high-limit, shutting the burners down. On a large home with more than one system, it's easy for one unit's filter to get neglected. We confirm airflow and whether the limit reset or failed.

How we diagnose it

Map which air handler and zone serves the cold area, so we diagnose the failed system and leave the working ones alone.
Determine whether it's a heat-production fault (igniter, sensor, valve, board) or a distribution fault (zone damper, blower).
Run a full ignition sequence on the affected unit and meter the igniter, flame sensor, and limit switch.
Test the zone panel and control board outputs before condemning expensive boards.
Meter carbon monoxide and inspect the heat exchanger on the affected gas furnace before we leave.

$75 diagnostic, credited toward any repair over $200. You get a written quote before any work begins.

Furnace Not Heating in Atherton: common questions

Do you service Atherton, and how fast can you get out here?

Yes, we work Atherton and the surrounding Peninsula homes regularly. We're based in San Ramon and cover the full Bay Area, with no-heat calls routed ahead of routine maintenance. Call (925) 999-4095 and we'll give you a real arrival window.

If only one wing is cold, do you have to replace the whole system?

Almost never. A single cold zone points to one air handler or one zone's controls, and that's usually a part-level repair on that unit. We don't quote a whole-house replacement for a localized fault. The $75 diagnostic is credited toward any repair over $200, and the written estimate spells out exactly which system needs what.

Why does one zone blow cold air while the rest of the house is warm?

Two likely causes. Either that zone's air handler isn't firing, which points to the igniter, flame sensor, valve, or board, or the furnace is firing fine but a stuck zone damper is blocking the heated air from reaching that zone. We confirm which one it is before quoting, because replacing a damper motor and replacing a control board cost very different amounts.

Nearby and related

Furnace Not Heating near Atherton: Menlo Park · Palo Alto .

This is usually a furnace repair in Atherton job. See our furnace repair overview or the Atherton service area.